Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as an energy source for electric vehicles (EV) and hybrid electric vehicles (HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel.
Small-sized mobile devices use one or several small-sized battery cells for each device. On the other hand, middle- or large-sized devices, such as vehicles, use a middle- or large-sized battery module having a plurality of battery cells electrically connected with each other because high output and large capacity are necessary for the middle- or large-sized devices.
Preferably, the middle- or large-sized battery module is manufactured with small size and small weight if possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell of the middle- or large-sized battery module. Especially, much interest is currently generated in the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the weight of the pouch-shaped battery is small and the manufacturing costs of the pouch-shaped battery are low.
FIG. 1 is a perspective view typically illustrating a conventional representative pouch-shaped battery. The pouch-shaped battery 100 shown in FIG. 1 is constructed in a structure in which two electrode leads 110 and 120 protrude from the upper and lower ends of a battery body 130, respectively, while the electrode leads 110 and 120 are opposite to each other. A sheathing member 140 comprises upper and lower sheathing parts. That is, the sheathing member 140 is a two-unit member. An electrode assembly (not shown) is received in a receiving part which is defined between the upper and lower sheathing parts of the sheathing member 140. The opposite sides 140a and the upper and lower ends 140b and 140c, which are contact regions of the upper and lower sheathing parts of the sheathing member 140, are bonded to each other, whereby the pouch-shaped battery 100 is manufactured. The sheathing member 140 is constructed in a laminate structure of a resin layer/a metal film layer/a resin layer. Consequently, it is possible to bond the opposite sides 140a and the upper and lower ends 140b and 140c of the upper and lower sheathing parts of the sheathing member 140, which are in contact with each other, to each other by applying heat and pressure to the opposite sides 140a and the upper and lower ends 140b and 140c of the upper and lower sheathing parts of the sheathing member 140 so as to weld the resin layers thereof to each other. According to circumstances, the opposite sides 140a and the upper and lower ends 140b and 140c of the upper and lower sheathing parts of the sheathing member 140 may be bonded to each other using a bonding agent. For the opposite sides 140a of the sheathing member 140, the same resin layers of the upper and lower sheathing parts of the sheathing member 140 are in direct contact with each other, whereby uniform sealing at the opposite sides 140a of the sheathing member 140 is accomplished by welding. For the upper and lower ends 140b and 140c of the sheathing member 140, on the other hand, the electrode leads 110 and 120 protrude from the upper and lower ends 140b and 140c of the sheathing member 140, respectively. For this reason, the upper and lower ends 140b and 140c of the upper and lower sheathing parts of the sheathing member 140 are thermally welded to each other, while a film-shaped sealing member 160 is interposed between the electrode leads 110 and 120 and the sheathing member 140, in consideration of the thickness of the electrode leads 110 and 120 and the difference in material between the electrode leads 110 and 120 and the sheathing member 140, so as to increase sealability of the sheathing member 140.
However, the mechanical strength of the sheathing member 140 is low. In order to solve this problem, there has been proposed a method of mounting battery cells (unit cells) in a pack case, such as a cartridge, so as to manufacture a battery module having a stable structure. However, a device or a vehicle, in which a middle- or large-sized battery module is installed, has a limited installation space. Consequently, when the size of the battery module is increased due to the use of the pack case, such as the cartridge, the spatial utilization is lowered. Also, due to the low mechanical strength, the battery cells repeatedly expand and contract during the charge and the discharge of the battery cells. As a result, the thermally welded regions of the sheathing member may be easily separated from each other.
There have been proposed some technologies for covering the outer surfaces of the pouch-shaped battery cells using a cell cover so as to secure the safety of the battery cells.
For example, Japanese Patent Application Publication No. 2005-108693 discloses a cell cover including a pair of elastic parts, having the same elasticity, for supporting opposite major surfaces of a plate-shaped laminate battery cell.
The disclosure proposes a structure to elastically press the opposite major surfaces of the battery cell using the cell cover which is bent in a concave shape. However, the overall size of the battery cell is inevitably increased due to the additional attachment of the cell cover to the outer surface of the battery cell. Also, it is required that the battery cell be inserted into the cell cover with the above-stated construction. As a result, the assembly process is not easily performed, and therefore, mass production is difficult. That is, when the battery cell is forcibly inserted into the cell cover, excessive load is applied to the battery cell with the result that the battery cell may be damaged.
Meanwhile, since a battery module is a structural body including a plurality of battery cells which are combined with each other, the safety and the operating efficiency of the battery module are lowered when overvoltage, overcurrent, and overheat occurs in some of the battery cells. Consequently, a sensing unit for sensing the overvoltage, overcurrent, and overheat are needed. Specifically, voltage and temperature sensors are connected to the battery cells so as to sense and control the operation of the battery cells in real time or at predetermined time intervals. However, the attachment or the connection of the sensing unit complicates the assembly process of the battery module. In addition, short circuits may occur due to the provision of a plurality of wires necessary for the attachment or the connection of the sensing unit.
In addition, when a middle- or large-sized battery module is constructed using a plurality of battery cells or a plurality of unit modules each of which includes a predetermined number of battery cells, a plurality of members for mechanical coupling and electrical connection between the battery cells or the unit modules are needed, and a process for assembling the mechanical coupling and electrical connection members is very complicated. Furthermore, there is needed a space for coupling, welding, or soldering the mechanical coupling and electrical connection members with the result that the total size of the system is increased. The increase in size of the system is not preferred in the above-described aspect Consequently, there is high necessity for a battery module that is compact and structurally stable.